Disk drive memory systems store digital information on magnetic disks, which typically are divided into concentric tracks, each of which are in turn divided into a number of sectors. The disks are rotatably mounted on a spindle and information is accessed by read/write head assemblies mounted on pivoting suspension arms able to move radially over the surface of the disks. The radial movement of the head assemblies allows different tracks to be accessed from the inside diameter to the outside diameter of the disks. Rotation of the disks allows the read/write heads to access different sectors of each track.
In general, head assemblies are part of an actuator assembly, which also typically includes a suspension assembly, a flexure member and an arm, among other things. Head assemblies typically include a magnetic transducer to write data onto a disk and/or read data previously stored on a disk. Head assemblies also typically include a body or slider having an air bearing surface which, in part, functions during operation to position the magnetic transducer a specified distance from the surface of the spinning disk. In general, it is advantageous to position the magnetic transducer as close as possible to the disk.
A primary goal of disk drive assemblies is to provide maximum recording density on the disk. A related goal is to increase reading efficiency or to reduce reading errors, while increasing recording density. Reducing the distance between the magnetic transducer and the recording medium of the disk generally advances both of those goals. Indeed, from a recording standpoint, the slider is ideally maintained in direct contact with the recording medium (the disk) to position the magnetic transducer as close to the magnetized portion of the disk as possible. However, since the disk rotates many thousands of revolutions per minute, continuous direct contact between the slider and the recording medium can cause unacceptable wear on these components. Excessive wear on the recording medium can result in the loss of data, among other things. Excessive wear on the slider can result in contact between the magnetic transducer and recording medium resulting in failure of the magnetic transducer or catastrophic failure.
In applications utilizing contact start/stop technology, when power to the disk drive is turned off, the suspension arm moves to the inner diameter of the disk and directs the head assembly to land on a specified area of the disk, commonly referred to as the Laser Texture Zone, located at the extreme inner diameter of the disk. At rest, the head assembly rests on the surface of the disk in the Laser Texture Zone. When power is turned back on, the disk starts to spin, generating a body of moving air above the disk that lifts the head assembly above the surface of the disk. The head assembly then is moved to the desired location relative to, and above, the spinning disk.
The Laser Texture Zone is designed to provide sufficient length and breadth to accommodate the landing of the head assembly onto the disk during power off, and to accommodate the lifting of the head assembly off of the surface of the disk during power on. The Laser Texture Zone obtains its name from its relatively rough surface with laser created bumps to reduce stiction of the recording head when at rest on the disk. Because of the interaction between the head assembly and disk, including the forces imparted during start and stop operations and the direct contact during power off, the Laser Texture Zone typically is not intended to store information.
Optimally, the head assembly contacts the disk only within the Laser Texture Zone. The remainder of the disk, other than the Laser Texture Zone, is designed to optimize the recording, storing and retrieving of information. This remainder of the disk, referred to as the Data Zone, extends outwards to the outside diameter of a typical disk. To protect the disk from impact forces and stiction forces from the head assembly, among other things, the base magnetic layer of a disk typically is covered with a protective layer of carbon overcoat and an outer layer of lubricant.
A more recent development in head-disk assembly tribology is dynamic load/unload technology. Rather than designing the head assembly to land on, rest on and lift off of the surface of the disk in the Laser Texture Zone, dynamic load/unload technology suspends the head assembly on a ramp, typically located in proximity to or outside of the outside diameter of the disk, although it may be located at any fixed radius. More specifically, a ramp is built into the housing of the magnetic disk drive assembly overhanging the outer most portion of the disk or adjacent the outside diameter of the disk. A tab or an extension of the suspension arm rests on the ramp, thereby suspending the head assembly, either above the disk or just beyond the outside diameter of the disk. Even at rest, the head assembly is designed to not be in direct contact with any part of the disk. When the power is turned on and after the disk is spinning, the head assembly is designed to move down the ramp and fly above the spinning disk.
Dynamic load/unload technology essentially has replaced contact start/stop technology in mobile products, such as lap top computers, and is in the process of doing so in non-mobile products, such as desktop and server computers. Dynamic load/unload technology is also essential technology in removable media drives, such Zip® drives. However, a limiting factor on the use of dynamic load/unload technology is the extent to which the composition and construction of the load/unload ramp itself impacts the design, manufacture and reliable operation of the disk drive assembly. A preferred ramp material has the properties of low wear, high mechanical stability, high moldability and low cost.
These desired properties have not been optimized in any one material or combination of materials. That is, a material with relatively low wear, low cost and high moldability may have poor mechanical stability. A different material with high mechanical stability may have high wear or high cost.
For example, the ramp may generate wear particles from the repeated landings and take-offs of the head assembly. Such wear particles may settle on the surface of the disk and cause the head assembly to fly at a greater height than desired. Flying heights that are too high lead to higher error rates for both reading and writing data, while flying heights too low lead to disk wear and possible assembly head crashes. Accumulated wear particles may also pass under the slider and lead to thermal asperities or high-fly writes. As such, the ramp should be constructed of a material with low wear.
Another characteristic of a preferred ramp material is low deformation, also referred to as good mechanical stability, which generally includes low warpage, low thermal expansion, low water adsorption, high strength, high stiffness, low creep and low shrinkage. Deformation of the ramp material is a significant contributor in the very tight vertical dimensioning design for engagement of the load tab and ramp. In a worst case scenario, ramp deformation due to expansion, contraction or creep may cause the ramp to contact the spinning disk or cause the load tab to contact the front edge of the ramp.
Robust processing, also referred to as moldability, generally is the capability of the ramp material to be shaped or formed to the precise dimensions desired, stored, transported and installed in the disk drive assembly. Moldability is particularly important for fine features, such as ramp tips, which must be molded consistently. Also, better moldability includes process time, since a part that takes longer to mold is more expensive. A higher the level of moldability results in a higher yield, i.e., a higher number of ramps that are successfully installed in a disk drive assembly and a lower number of ramps and a lower amount of ramp material that must be recycled or discarded.
Existing disk drive products have used a variety of materials and combinations of materials for load/unload ramps. These materials typically are thermoplastic polymers, such as Delrin, an acetal homopolymer available from E.I. duPont de Nemours & Co. of Wilmington, Del. (“duPont”) or Vectra, a liquid crystal polymer with Teflon fill, available from Ticona, a subsidiary of Celanese, A.G. of Germany (“Ticona”). Each of these materials has performance drawbacks as a material for a load/unload ramp. For example, Delrin has relatively low wear, low cost and robust processing, but has relatively poor mechanical stability, particularly thermal expansion and shrinkage. Vectra has relatively higher wear, which negatively affects reliability of the disk drive assembly, and is relatively much more expensive. Other existing materials and combinations of materials have similar types of tradeoffs between desirable and undesirable characteristics.
As such, a need exists for improving the composition and characteristics of the load/unload ramp utilized in a magnetic disk drive assembly incorporating dynamic load/unload ramp technology by improving its mechanical stability, wear, cost and/or moldability.